Internal combustion (IC) engines have been used for many years to convert chemical energy stored in fuels to mechanical energy. The main components of an IC engine are a cylinder in an engine block, a reciprocating piston in the cylinder, a rotatable crankshaft, and a connecting rod, which transfers energy from the reciprocating piston to the rotating crankshaft.
The best automotive IC engines run at about 26% thermal efficiency at peak operating conditions. The remaining energy is lost through convection to the engine block, heat in the exhaust gas and unburned fuel. Almost half of the available energy from the fuel is lost through the heat convected to the engine block and removed by the engine radiator. About 8% of the potential energy is lost due to incomplete combustion of fuel in the cylinder.
Industry has long sought ways to reduce the heat transfer from the combusting gases to the engine block to get more mechanical power, increase life of engine parts, and obtain higher combustion temperature. For example, thermal barrier coatings have been applied to the inside of the cylinder, but those coatings rubbed off as the piston reciprocated in the cylinder.
In addition to saving fuel, reducing the heat transfer from combusting gases to the engine block also has application for the military where reduced thermal signatures are critical.
For many years, gas turbine engines have used “film cooling”, i.e., cooling with a flowing film of cool air, to reduce transfer of heat by convection from combusting gases to the combuster walls. The flowing film of cool air against the protected surface permits operating the gas turbine at higher, and therefore more efficient, temperatures. Film cooling is also used on the outside of the turbine airfoils to achieve higher operating temperature and efficiency.
The inherent disadvantages of IC engines (both Diesel and gasoline) are reduced by the present invention, which uses film cooling to reduce heat transfer to the engine block, increase life of engine components, improve fuel combustion efficiency, and increase engine compression ratio. Film cooling applied to IC engines in accordance with this invention provides increased engine combustion temperature, increased shaft power, reduced fuel flow to the engine, or any combination thereof.